1. Field of the Invention
This invention relates to a contact material for a vacuum circuit breaker, which is excellent in large current breaking property and high voltage withstand capability.
2. Description of Prior Art
The vacuum circuit breaker has various advantages such that it is free from maintenance, does not bring about public pollution, is excellent in its current breaking property, and so forth, on account of which the extent of its application has become widened very rapidly. With this expansion in its utility, demands for higher voltage withstand property and larger current breaking capability of the vacuum circuit breaker have become increasingly high. On the other hand, the performance of the vacuum circuit breaker depends, to a large extent, on those factors to be determined by the contact material placed within a vacuum container for the vacuum circuit breaker.
For the characteristics of the contact material for the vacuum circuit breaker to satisfy, there may be enumerated: (1) large current breaking capacity; (2) high voltage withstand; (3) small contact resistance; (4) small melt-adhesion; (5) low consumption rate of the contact; (6) small breaking current; (7) good workability; (8) sufficient mechanical strength; and so on.
In the actual contact material, it is fairly difficult to satisfy all of these characteristics, and general circumstances at the present time are such that use is made of a material which meets particularly important characteristic depending on its utilization at the sacrifice of other characteristics to some extent. For instance, the contact material of copper-tungsten alloy as disclosed in Japanese Unexamined Patent Publication No. 78429/1980 is excellent in its voltage withstand capability, so it is frequently employed for a load-break switch or a contactor. However, it has a disadvantage such that its current breaking property is inferior.
On the other hand, the contact material of copper-chromium alloy as disclosed, for example, in Japanese Unexamined Patent Publication No. 71375/1979 has been widely used for a circuit breaker or the like owing to its excellent current breaking property, but its voltage withstand capability is inferior to that of the above-mentioned contact material of copper-tungsten alloy.
As described in the foregoing, the conventional contact materials for the vacuum circuit breaker have so far been used in taking advantage of various properties they possess. In recent years, however, requirements for large current breaking capability and higher voltage withstand property of the vacuum circuit breaker have become more and more stringent with the result that such conventional contact materials tend to be difficult to satisfy the required performance. There has also been a demand for the contact material having more excellent performance against size-reduction in the vacuum circuit breaker. Ideally, therefore, a contact material having more excellent current breaking property than that of the above-mentioned copper-chromium alloy contact, and more excellent voltage withstand capability than that of the copper-tungsten alloy contact is desired.